After Doctor Eggman's latest attempt at controlling Sonic's world, it left the planet in disrepair and disease. What's left of the population is scared and hostile to outsiders, and they don't believe in heroes anymore. Sonic can't help them believe. He hardly believes, himself. Suffering injuries and a near defeat, he spent the last year of the apocalypse recovering with Tails, unable to communicate with his other allies. But then comes the word of three cities. Uninfected, where the world might recover from Eggman's blight. These cities might be what Sonic and Tails need to manufacture a cure and save their beloved planet. Only problem? They'll have to fight through a world of infected and hostile Mobians to get to them.